In a room upstairs at the New Horizons Youth Centre in Euston, central London, the charity's director, Shelagh O'Connor, is giving me an exhaustive explanation of their work. The centre seems to do everything: it helps homeless young people source hostel spaces, offers education and training programmes, counselling, health advice and cookery, arts and drama workshops. There are sports and gym facilities. There's a recording studio.

To her left, Mitch Winehouse sits listening. He wears a suit and occasionally chips in. "You can't allow young people to sleep rough in the streets," he frowns. "What's going on in our country – in my opinion the greatest country in the world – is nothing short of a disgrace," he says, sounding not unlike the London cabbie he used to be, before his daughter Amy got famous, her life went haywire and he had to give it up. He tried to keep working, but the stress of being the father of the most famous wayward daughter in the country was too much: he started having anxiety attacks and ended up seeing a psychiatrist, "which I needed and kind of sorted me out for a while".

He is still a licensed cab driver, but he hasn't gone back to driving the taxi. Instead, he finds himself working for the Amy Winehouse Foundation, the charity he decided to set up in the wake of her death last July. He says he had the idea on the plane home from the US. He had been in New York, promoting his own singing career, when she was found dead from alcohol poisoning in her Camden home. "Coming back on the plane, it was awful. It was dreadful. I had my manager Trenton with me, and Amy's manager Raye. They were very upset, but I was …" His voice tails off. "I was OK. I was obviously in shock. And all I kept thinking of was the foundation. Although I was OK coming on the flight from America, I thought to myself, I'm actually going insane. I'm actually losing my mind. I could feel myself slipping away. And then, the minute I stepped off the plane and went to her house and there were hundreds and hundreds of people there, I got a sense of how I could deal with it, how I could overcome this."

Has it helped? "It's saved my life. It's saved my life. Nobody should know what it feels like to lose a child. I lost my dad when I was 16; he was 43. We were very close. But losing a parent is not like losing a child. It's worse than awful. But the more I spoke to people about the charity, about helping people, especially people Amy would have wanted to help, it became my lifeline, so to speak."

So the foundation gives money to New Horizons, the Pilion Trust's Crashpad homeless shelter and charities dealing with addiction. It funds a scholarship to the Sylvia Young Theatre School, where Amy studied, and supports children's hospices. "Amy would love that. She loved babies. She didn't know she was going to die, obviously, so she didn't leave a list of people she wanted to help, so we have to second-guess."

I had assumed the charity was funded by her estate, but no: "whatever money has been left to Amy, I want to keep that for my son and his future children, you know, I want Amy's family to benefit from that." Instead, it raises funds, which explains why Winehouse has written a book entitled Amy: My Daughter that retells her story from his perspective. It skips through a childhood marked only by his divorce from her mother, Janis, and her early success with her 2003 debut album Frank, and then plunges headlong into what happened next: the global fame that followed 2006's Back to Black and her virtually concurrent descent into drug addiction and alcoholism – laying the blame for her crack and heroin use squarely at the door of her ex-husband, Blake Fielder-Civil, "the biggest low-life scumbag that God ever put breath into".

"Of course, even though there's a big sticker on the book saying 'all author's proceeds to the Amy Winehouse Foundation,'" he frowns, "people are still saying I'm lining my own pockets or whatever, which is obviously not true."

He seems wearily resigned to public criticism. There was a lot of it when Amy was alive: he was so visible, giving quotes to the papers, being photographed by her side, even relaunched his own singing career in 2010. The latter certainly looked a little strange from the outside – his daughter publicly struggling with addiction, Winehouse releasing an album on the back of her fame – but he says it was Amy who pushed him into it. "Some people think I've only just brought the album out after Amy passed away. But she was driving me mad about it: she'd get me onstage to sing with her; say: 'Dad, you've got to do an album.' I'd say: 'Do me a favour, Amy, no one's interested.' Then she got ill so it was just put on the back burner. But as she started to get better, part of her recovery was to help me, so she'd pick songs for me to sing."

Aside from making money, he says he thought writing the book might make him feel better, but doesn't seem sure if it has. "It did for a few months. What I found extremely difficult was reading the book back. You know, the first draft. It was horrible. It really, really was awful."

You can see why. The overwhelming sense of her family's helplessness in the face of her addiction makes Amy: My Daughter a deeply harrowing read. "Her mum, her brother, my sister, my wife – none of us had a clue what to do. All well-meaning, but you know, we'd stand there and go, what the fuck do we do? What are we going to do? And then we'd bring outside influences in, doctors and everyone: please help us. And if there were six people in there, all experts in what to do, they'd have six different opinions."

To his immense credit, Winehouse seems to have resisted the temptation to whitewash his daughter's story, to try to posthumously beatify her. He laughs mirthlessly when I mention it. "She was a real person, she is a real person and she did what she did. Whatever I say about Blake, he didn't force the drugs down her mouth. What's the point in trying to change … everyone knows that. Like most people's kids, one minute she was wonderful, the next she was bloody horrible."

Today, when he talks about her, his eyes keep brimming and his voice cracks with emotion. Occasionally, he talks about her in the present tense, before swiftly correcting himself. "She's the greatest living female jazz singer," he says at one point, then lowers his eyes. "Excuse me. She was the greatest living female jazz singer." I feel a bit wretched asking him about her, as though I am probing a wound that clearly hasn't healed: it's less than a year since she died. No, he says, he wants to do it, wants to sell the book, make more money for the charity.

On the most basic level, he says, the charity gives him something to do. Looking after his daughter had become a full-time job. Aside from the helplessness, the grinding, numbing relentlessness of it might be the most striking thing about his book. He was round her house at all hours, checking up on her, throwing out drug dealers and hangers-on, trying to talk her into getting help, ferrying her to and from a succession of doctors' appointments and private hospitals, delivering her supplies of the heroin substitute Subutex. Or he was on the computer, reading up on addiction and potential treatments. Or he was waging war with Fielder-Civil and his family in the tabloids and dealing with her various legal problems: court appearances for assault, an arrest for possession, visas to the US that kept being denied because she kept failing the drug tests. After she died, he says, he felt so lost that he found himself texting her, asking when she was coming home.

"My whole life was consumed with it. But what else can you do? When your kid is in trouble, you've got to do whatever you can. But it was all consuming. There were times by me going round … [his voice falters] Amy would have died four years ago. There was one particular incident four years ago when, by a complete fluke, I went into her room five minutes after someone else had checked on her, and had I not been there, she'd have died." He found her having a seizure, brought on by an adverse reaction to some temazepam she had taken. "Had she died at that point, I'd have held my hands up and said: 'Well, listen, she's very ill and …' But she didn't. Somehow, she got herself out of that. She was drug-free for three years. And that's what makes it so hard when she did pass away; she was doing so well."

It's a subject that Winehouse returns to again and again during our conversation: that she was getting better, that she had beaten her drug addiction three years before her death and he felt she would do the same with alcohol, despite the fact he knew that alcohol "would kill you quicker than heroin would have", despite the fact that on bad days, she would wake up, drink a bottle of wine, then go straight back to bed. "It's true she was drinking to seek oblivion. I don't know what she was trying to escape from. I mean, everything was going better, she'd somehow got rid of Blake, she had a great new boyfriend, a great relationship with her family. The last six weeks of her life – five and half of them were spent not drinking. Her last 18 months were the best of her life." He laughs mirthlessly again. "If you take the bit out where she died, everything was better."

He says he's "not proud of some of the things I did". He used to lose his temper, punching the walls of her house, kicking her jukebox until "there was a big dent in it". "I'm a volatile person, so I'd go in and I would see she was in a state and I'd start screaming and shouting, and that doesn't help anybody." He occasionally became violent with the people around her. Legend has it that when he found Pete Doherty backstage at one of her gigs, he smashed him over the head with his guitar. On one occasion, he kicked Fielder-Civil, something he says he later heard Winehouse bragging about to a friend on the phone: "My dad done his nut, he kicked Blake up the arse, it was fantastic."

On another, he got into a fight with Fielder-Civil's parents. They accused him of grassing their son up to the police when he was arrested on charges of perverting the course of justice, after Fielder-Civil paid a pub landlord he had beaten up to drop charges of grievous bodily harm. "They came to the house and we ended up having a fight. There's three of them against me, and Amy's holding on to my legs and my trousers fell down. There was a big window in the flat and all the paps had been there taking pictures of him being arrested. I thought, they've still got to be there, and now they've got a picture of me fighting his parents with my trousers around my ankles." He laughs darkly. "But they weren't. That would have been the shot of the year."

Throughout it all, his daughter kept working, albeit sporadically and erratically. She played gigs that frequently ended in disaster, because she came on stage hours late, or was too drunk to perform. She embarked on two tours that had to be cancelled: one in November 2007, another a month before her death that ended after just one date in Belgrade, where she forgot the words to her songs, the names of her band, even what country she was in.

At the time, a lot of people suggested it all smacked of exploitation, that someone somewhere had a financial interest in forcing a desperately ill woman to work, but Winehouse says the opposite was true. "The whole thing is, she wanted to work. She felt that work was her salvation at that time. She felt that by working, she was distracted. She'd rehearse and she'd be out on the road with her friends and there was nobody there who would countenance any kind of class A drug-taking. Her friends used to phone me up, screaming at me: 'Why are you letting her go onstage?' But this is after me speaking to the doctors and them saying: 'It's a good thing for her to get onstage, she's got something to focus on, she's got something to look forward to.' I mean, the bottom line is that it was her choice and whatever decisions I made are irrelevant. I never made the decisions. She made them. The only decision we made was to pull the tours."

Amy duetting with Mitch Winehouse at his 60th birthday party in 2009. Photograph: Optic Photos Ltd

He thinks the problem was that Amy, despite her gobby front, suffered from stage fright. "Not to an acute extent, but she needed a drink before she went on, which was a problem because the management wouldn't give her anything to drink and then there would be arguments and, you know, "Is she going on or isn't she?" In later years, it was compounded by the fact that she felt trapped by her most famous songs. She didn't want to sing Back to Black or Love is a Losing Game because they reminded her of Fielder-Civil. But, understandably, given the chaos of her personal life, she hadn't written anything to replace them. "She said to me many times: 'I can't do these songs any more, Dad.' I said: 'Well, write some new ones then. Or do covers. People just want to hear you sing. You know, do your jazz stuff. Get up there and sing a nursery rhyme; they'll pay £100 to come and see you. They just want to see you, they want to see you enjoying yourself. There's no point in getting up there and singing songs that make you cry. Sing The Nearness of You.'" He sighs. "Lovely songs she could sing: Black Magic, Fly Me to the Moon. But those other songs were really a millstone around her neck. I can't listen to any of them."

That was a dark time, he says, before returning to the theme of how much better he thought she was doing before she died. He had insisted she was drug-free after her death and no one believed him until the postmortem. He talks about how tidy she had become: "When she was on drugs, the floor was her wardrobe, but towards the end of her life, if there was an Olympic sport in folding clothes, she would have won a gold medal."

On the last night of her life, she wasn't depressed, he insists. The last person to see her alive, a security guard, said she was singing and playing the drums, "and you wouldn't do that if you were depressed". She and her new boyfriend, the film director Reg Traviss, were talking about marriage, he says. "They were talking about kids. You know, Reg is heartbroken, because he knows what would have happened." His voice cracks again and he takes a deep breath. "He was going to be my son-in-law. We're still very close. We've got to the point where we can laugh about Amy's antics, about the great times we had." He sighs. "What a lovely girl. What a lovely, funny girl. It's a tragedy. But I've got to make the best of it. What do I do? Do I dig a hole and dive in it, which I felt like doing sometimes? Or do I come here, sit with these wonderful people at the charities and try to make a difference? That's what we're trying to do."